Clot in morphology

Clot in morphology

What does a clot mean in morphology? Why the test cannot be performed? Why has there never been a clot in the test tube, and suddenly there is?

The patient goes to the collection point, has blood taken, everything is fine, and in a few hours it turns out that he will not receive the result and has to take blood again. What is a cause of it? I will try to answer these questions in the way I like – pictorially, so that it is simple, clear and transparent.

Blood collection tube

anticoagulant i blood probe

Simply put, this is the test tube used to perform the blood count. Importantly – before taking blood from the patient, it is not empty at all! It contains a mysteriously named substance – ANTICOAGULANT.

The anticoagulant can be in a liquid form (at the bottom of the tube) or coated on the walls. The latter method of placing it in a test tube enables faster mixing of biological material with the anticoagulant.

What is this anticoagulant for?

The blood count can be performed only from whole blood, and it is well known that the blood clots after it leaves the blood vessel. And it is precisely this clotting that is prevented by the anticoagulant – it is thanks to him that the blood in the test tube remains in the same liquid form as it has in our body. In morphological test tubes, the most common anticoagulant is EDTA, i.e. sodium edetate. Some patients may have EDTA antibodies that make it impossible to test with an EDTA tube.

Blood sampling for complete blood count

patients blood

In order to perform a blood count, the collector selects the appropriate test tube. It is usually a test tube with a lavender-colored stopper. Some manufacturers deliver tubes in other colors, e.g. pink. Immediately after blood collection, a very important moment takes place – mixing the patient’s blood with the anticoagulant. And it is at this point that a clot is most often formed in the test tube.

The mixing of the patient’s blood with the anticoagulant and the blood clot in the morphology

blood mixing

Correct, thorough mixing of the patient’s blood is a very important step. If the person collecting the blood mixes the material in a sloppy manner or at all – then the patient will not receive a valid marking. The material is mixed by gently flipping it up and down – as in the diagram above. At the end of this activity, we obtain a homogeneous fluid.

properly mixed blood

If the sample is properly mixed, we obtain a homogeneous mixture of blood and anticoagulant. If the sample is mixed incorrectly – a clot or clots appear. They can take many forms – from large clots filling the entire tube to tiny, barely noticeable “clots”. The clot is made up of blood cells, i.e. cells, the number of which is assessed during the completion of the blood count. Sometimes it happens that the patient asks: Can’t you pull this clot out and do a test? Well no. Why? I provide an explanation later in this post.

clot in morphology, drawing blood

A large proportion of the clots are detected before the test is performed. However, if a blood sample is applied to the device and the test is performed, we will obtain a test result inconsistent with the patient’s clinical condition. The apparatus will evaluate depleted blood instead of wholesome blood containing all morphotic elements, as a large proportion of the blood components have been used to form a clot.


If we took a clot from the tube with the patient’s blood, we would obtain incorrect results (inconsistent with the facts). The cells that should be in the test tube are in the clot. The only solution is to draw blood again.

The formation of a clot in the test tube affects basically all blood count parameters. However, the most important changes include: reduction in the number of erythrocytes, hemoglobin, platelets, leukocytes and hematocrit. The separation of white blood cells (WBC) is impaired. This result is NOT SUITABLE for reporting to the patient.

Clot after analysis, clot before analysis

What does a clot mean before and after the analysis? This information is irrelevant to the patient. Whether it will be a clot before or after the analysis – he has to go to the blood collection again. Re-collection does not involve any additional costs, the test is performed at the expense of the laboratory. After the analysis, the clot is the clot detected after the test, before the analysis – even before the tube is inserted into the apparatus – such information is crucial in the statistics and reports conducted in the laboratory.

Clot in morphology – summary

The most common cause of a blood clot in the blood count is an error in the preanalytical phase – at the time of blood collection. The clot is not removed from the tube, and no examination is performed. Blood needs to be drawn again. All this is for the benefit of the patient – to obtain a result consistent with his clinical condition.

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Disclaimer: This page is for informational purposes only. Conversion rates have been compiled based on publicly available information. All information should be confirmed and verified. The data on the site is not a substitute for professional medical advice. Any information, result, conversion should be consulted with a doctor.

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